C is a factor for expressing the current flow rate for a battery based on its capacity:
For a 10Ah battery 1C = 1 x 10 =10A
For a 20Ah battery 1C = 1 x 20 = 20A
For a 5Ah battery 2C = 2 x 5 =10A
For a 34Ah battery 0.2C = 0.2 x 34 = 6.8A.
Individual C rate for a cell is 1 x it's mah rating.
Samsung 25R 2500mah & 20a max rated, 8c capable . 1c is 2500mah, 8 x 25 = 20a.
Samsung 29E 2900mah & 8.7a max rated, 3c capable. 1c is 2900mah, 3 x 29 = 8.7a.
The C rating is different for each cell so the manufacturers specs need checking for max charge and discharge rate. The lower C rate overall used for a cell group in parallel the longer the life span might be, life span is also dependant on discharge rate and how deep one goes beyond 3.2/3.3v per cell.
The more cells in parallel means each cells C rating is divided so one can use a slightly higher charge rated.